1. Field of the Invention
This application concerns a thermal engine with the capability to store and controllably release energy and which is particularly adaptable to free bodies which move vertically in a fluid medium, typically in the ocean.
2. Discussion of the Background
Bodies are commonly moved vertically through the ocean, for example instruments which measure the properties of the interior of the ocean at one or more depths, and transit to the surface for recovery, radio telemetry of stored data, etc.
The design of such bodies involves two problems. First, the motion from deep in the ocean to the surface and return. The work required is designated as the driving force F times the distance d through the water (i.e., work=F.times.d), and several approaches to generating the driving force are commonly used. For example, a motor/propeller system or a system of movement of seawater ballast from inside the body to outside, thus changing the density of the body, is known. Also known is a system of transferring oil or other fluids between a reservoir inside the body to a flexible external bladder, thus changing the specific volume of the body. This may include jettisoning of fluid or solid bodies of a density greater or less than a secondary body, or the transfer of gas from a storage reservoir inside the body to a flexible external bladder to ascend, and jettisoning the gas for descending.
For example, the ocean instrument commonly called ALACE (Autonomous Lagrangian Circulation Explorer) uses a electro-hydraulic system as follows. To ascend (i.e. gain buoyancy), oil from an internal reservoir is pumped to a flexible external reservoir via a hydraulic pump powered by an electric motor. To descend, an electrically operated hydraulic valve opens and allows oil to flow from the external to an internal reservoir. Both the motor and valve draw power from a battery pack and are controlled by an electronic controller.
Most of these approaches have been used, and are suitable for providing the driving force to move the body through a column of water.
Once the body reaches the surface of the ocean a second problem is frequently encountered. The body needs a certain buoyancy to expose its antenna, relocation aids, reflectors, etc., and this buoyancy is often greater than can be readily provided by the propulsion system which brought it to the surface.
Stated another way, the body, on arrival at the surface has very little buoyancy, and if disposed in a surface wave field, it will frequently be below the surface.